"Protection from instants" means instant spells can't target it, damage that would be dealt to it by instant sources is prevented, and it can't be the target of abilities of instants (such as Haunt).

2/1/2006

Protection from instants works only while Petrified Wood-Kin is on the battlefield. It can be targeted by instant spells or abilities of instant cards while it's on the stack or in any other zone but on the battlefield.